# chemistry

how do you solve this problem??

What is the original molarity of a solution of formic acid (HCOOH) whose pH is 3.26 at equilibrium?

the answer is 2.3 x 10^-3M.

1. 👍
2. 👎
3. 👁
1. HCOOH ==> H^+ + HCOO^-

pH = 3.26, solve pH = -log(H^+) for(H^+).
Then [(H^+)(HCOO^-)]/[(HCOOH)-(H^+)]=Ka

I don't know what you are using for Ka. Using 1.77 x 10^-4 for Ka, which I obtained from an old book of mine, I arrived at 0.00226 M.

1. 👍
2. 👎
2. First, the idea of pH = -log [H+] where [H+] is the molarity of H+
This can be rearranged to:
[H+] = 10^-pH

so from the pH you know the molarity of [H+] = 10^-3.26, which equals 5.4954 * 10^-4 M

Next, the idea of a weak acid and Ka. A weak acid has the form:
HA --> H+ + A-
and Ka = [H+][A-]/[HA]

The Ka for formic acid is 1.7 * 10^-4

Set-up the table
HA H+ A-
Initial x 0 0
Final x - 0.0005954 0.0005954 0.0005954

The x is the original molarity of the acid. The 0.0005954 is the molarity of the H+ as told by the pH. Whatever amount of H+ is made is the same as the amount of A-, and the amount of HA gone. So:

1.7 * 10^-4 = [0.0005954] * [0.0005954]/ [x -0.0005954]

1.7*10^-4 * x - 9.89*10^-8 = 3.545 * 10^-7

1.8*10^-4 * x = 4.534 * 10^-7

x = 0.0023 M

Pretty close to the answer they got. I may have messed up using this computer's calculator, but that's the process:

1. Use pH to get molarity of H+
2. Set-up a table to get the values for HA, H+ and A-
3. Plug values into Ka equation

1. 👍
2. 👎

## Similar Questions

1. ### Chemistry

what volume of concentrated 18M H2SO4 is required to prepare 250mL of a 6.0M solution? how would you solve this problem? i know it has something to do with the molarity formula but no idea how to apply it

2. ### Chem

What is the original molarity of a solution of ammonia whose pH is 11.11 okay i tried to convert to pOH- so i got 2.89 and then to [OH]=1.288e-3 and then solve using Kb=1.8e-5 whats going wrong???

3. ### Chem Help

With the same initial solution of 0.75 moles formate and 0.85 moles formic acid to make a buffer solution. The Ka of formic acid is 1.8x10-4. You add 16g hydrobromic acid to this solution, what is the new pH? I tried making this

4. ### Chemistry

1.With the same initial solution of 0.75 moles formate and 0.85 moles formic acid to make a buffer solution. The Ka of formic acid is 1.8x10-4. You add 8g sodium hydroxide to this solution, what is the new pH? 2. With the same

1. ### Help Chem Buffer

1. With the same initial solution of 0.75 moles formate and 0.85 moles formic acid to make a buffer solution. The Ka of formic acid is 1.8x10-4. You add 8g sodium hydroxide to this solution, what is the new pH? 2. With the same

2. ### chemistry

Find the molar masses of the following compounds: 1. LiI 2. PbCO4 3. Mg(OH)2 4. (NH4)3PO4 Find the percent composition (percent by mass) of the given element in the following compounds: 1. Fluorine in AgF 2. Hydrogen in glucose

3. ### Algebra

Solve the equation. Identify any extraneous solutions. √a=-2 A.4 is a solution of the original equation. B.4 is a solution of the original equation. -4 is an extraneous solution***** C.-4 is a solution of the original equation.

4. ### Chemistry HW!!!

1. If I dilute 75 mL of 0.50 M CaF2 solution to a final volume of 375 mL, what will be the molarity of the resulting solution? 2. What will be the final volume of the solution be if I start with a 250 mL of 1.38 M MgCl2 solution

1. ### Chemistry

Calculate the molarity of Formic acid in a solution containing 44g of Formica acid in 470 g of nitrobenzene. The molar mass of Formica acid is 36g/mol

2. ### Chemistry Acid/bases

The concentration of H2SO4 in a solution is 3.20 10-6 M. Assume the acid dissociates completely in solution. What is the [H3O+] in the solution? What is the [OH-] in the solution? What is the pH of the solution? What is the pOH of

3. ### Chemistry

A solution is created by dissolving 13.0 grams of ammonium chloride in enough water to make 265 mL of solution. How many moles of ammonium chloride are present in the resulting solution? When thinking about the amount of solute

4. ### chemistry

What is th pH of a buffer solution made by dissolving 0.10 mol of formic acid, HCOOH, and 0.10 mol of sodium formate, HCOONa, in 1L of water? What is the molarity of a solution made by dissolving 3.4g of Ba(OH)2 in enough water to